Samples of Al-doped 4H-type and 6H-type materials were investigated by means of optically detected electron paramagnetic resonance. As well as known photoluminescence -detected electron paramagnetic resonance spectra, new optical absorption spectra were detected by measuring the magnetic circular dichroism. By means of magnetic circular dichroism absorption-detected electron paramagnetic resonance, the hyperfine interactions of all Al defects on 3 inequivalent sites in 6H-material and 2 sites in 4H-type material could be resolved. The effective electron spin of all of the Al acceptors which were observed was determined to be S = 1/2.

J.Reinke, S.Greulich-Weber, J.M.Spaeth: Solid State Communications, 1996, 98[9], 835-8